Needle-shaped pressure transducer



United States Patent Inventors Takewo Chiku Toyota-shi; Isemi lgarashi,Nagoya-shi, Japan Appl. No. 725,314 Filed Apr. 30, 1968 Patented Dec.29, 1970 Assignee Kabushiki Kaisha Toyota Chuo Kenkyusho Aichi-Ken,Japan Priority May 13, 1967 Japan No. 42/30476 NEEDLE-SHAPED PRESSURETRANSDUCER 5 Claims, 3 Drawing Figs.

U.S. C1 128/2.05, 73/398 Int. Cl A6lb 5/02 Field of Search l28/2.051 )M,2; 73/398, 398R References Cited UNITED STATES PATENTS 8/1953 Hathawayet a1. 128/205 2,799,788 7/1957 Fitzgerald et a1. 4. 73/398X 2,959,05611/1960 Traite et a1. 128/2.05X

3.038,465 6/1962 Allard et a1. 128/205 3,240,065 3/1966 Taber 73/398X3,337,844 8/1967 Baltakis 73/398X OTHER REFERENCES Angelakos, AmericanJournal of Medical Electronics. Oct-Dec. 1964. pp. 266-270(l282.05D)

Primary Examiner-William E. Kamm Attorney-Herman, Davidson and BermanABSTRACT: A transducer comprising a slender outer tube and a sensingmechanism therein, said tube being closed on its one end by a diaphragmand a plug of nonconstrictive material to sense a pressure, or otherforce, from the outside of the transducer pressure to said sensingmechanism, said sensing mechanism being disposed parallel to the axis ofsaid tube and including at least one sensing element of semiconductivematerial to convert said pressure when applied into a change in internalresistance by the piezoresistance effect. The transducer may be ofmicrominiature size and shaped as an injection neddle suitable forinsertion into a body vessel to convert and measure blood pressure, forexamplev NEEDLE-SHAPED PRESSURE TRANSDUCER The present invention relatesto a transducer device and more particularly to such a device utilizinga sensing element made from an electrical semiconductive material.

For measuring blood pressure of a living body, it has been usual toemploy a method of selecting parts adjacent the surface of a livingbody, such as blood vessels of veins or arteries, pressing said bloodvessels to temporarily stop the circulation of blood and therebydetecting the blood pressure by the pressing force (hereinafter calledthe Indirect Method). In such Indirect Method, the measured pressurefrequently does not fully conform to the pressure in the blood vesselsdue to resilient character of the living body thus pressed. Methods havebeen required, therefore, for directly measuring the blood pressure by apressure meter in contact with the blood itself and such methods arereferred to as the Direct Methods hereinafter.

Two Direct Methods have been known in one of which the skin of a livingbody is cut open and blood vessels are exposed, said blood vessels beingconnected to pipes leading to a measuring chamber, and the blood isintroduced to said chamber outside the living body whereby the pressurein said chamber is measured. In the second Direct Method, acontainer-type pressure transducer having two diaphragms is inserted inthe blood vessels of a living body. Such container-type pressuretransducer was invented by the present applicants and disclosed in theJapanese Patents Nos. 502,405 and 502,410. However, this method requirescutting and opening of a living body; thus it is not suitable forordinary pressure measurements except for pathological research, otherspecial work, or animal experiments.

The first Direct Method could not avoid the effect of resiliency of thepipe connected to the outside of a living body, and the effect offriction or pressure propagation of the pipe body to the interior of themeasuring chamber. The second Direct Method encounters difficulty in themanufacture of a pipe having an outer diameter less than 3mm and,therefore, it is difficult to obtain measurements of pressure inordinary living bodies.

It is a primary object of the present invention to overcome the defectsand disadvantages of conventional transducers as briefly outlined aboveand to provide much simpler means for measuring blood pressure, whichdoes not require the cutting or opening of the skin ofa body, and whichemploys a piercing or injection type needle as used in ordinarydiagnostic procedure.

A general object of the invention is to provide a new transducer havinga slender outer tube with a sharpened rigid open end portion to whichthe pressure to be measured is applied, and a slender cylindricalsensing mechanism including at least one sensing element ofsemiconductive material therein to sense a pressure or other force to bemeasured to axial direction of said sensing mechanism and convert thesame into an electrical signal.

Another object of the invention is to provide a transducer, having theabove described characteristics, in which the sensing mechanism has atube which forms an outer cylindrical wall, at least one sensingelement, disposed parallel to the axial direction of said tube and astrain sensing filler completely occupying the interior of said tube.

A further object of this invention is to provide a transducer, havingthe above-described characteristics, said outer tube being closed at theforward end by a filler, said sensing mechanism disposed in coaxialrelation to said outer tube, and secured to said filler by its one end.

A further object of this invention is to provide a pressure transducer,having the above-described characteristics, in which a sharpened edge isprovided at one end of said outer tube so as to form an injection needleand said sensing mechanism is provided in the interior space of saidinjection needle.

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The invention,itself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of specificembodimentswhen read in connection with the accompanying drawings,wherein like reference characters indicate like partsithroughout theseveral FIGS. and in which: i 7

FIG. 1 is a cross-sectional view of an embodiment;

FIG. 2 is a cross-sectional view oftheFIG. 1 embodiment slightlymodified; and I i v FIG. 3 is a cross-sectional view of another modifiedembodiment, the original of which is shown in FIG. 1.

Now referring to the drawings, and more particularly to FIGS. 1 and 2,wherein is shown a sensing mechanism designated as a whole by 5, andwhich includes a slender tube 1, a pair of strain sensing elements 3, 3formed as strips or bars of a semiconductive material, which aredisposed parallel to the axis of tube 1 and each having a terminal orelectrode 2 at each end, and filling material 4 surrounding the strainsensing elements 3 and filling the interior space of slender housingtube 1.

It is to be understood that when a force, or a pressure in a pressurizedmedium, is applied to one end of tube 1', the pressure or force istransmitted in the direction parallel to the axis of said slender tube 1through said filler 4, and is converted to an electric signal as byresistance variation due to the piezoresistive effect on thesemiconductive strain sensing elements 3.

In both FIGS. 1 and 2, a sensing mechanism 5, as abovedescribed isinstalled within rigid outer tube A which is provided with a sharpenededge or a sharpened end portion on its forward end so as to form ahypodermic injection needle. The sensing mechanism 5 is installed in ornear the sharpened open end portion of the outer tube A.

The rear portion (left in FIG. 1) of the sensing mechanism 5 is securedto the inner face of tube A by a spacer 6 which is a plug composed of arigid resin. The front portion (right in FIG. 1) of the sensingmechanism 5 is secured to a filler 7 closing the front open end of tubeA and which is composed of a nonconstrictive resin. A space 8 is leftbetween parts 6 and 7 across which extends the sensing mechanism 5spaced from the inner peripheral wall of tube A.

In the embodiment shown in FIG. 2, there is provided at the rear end ofthe sensing mechanism 5, a tube 9 of electrically insulating materialcemented to the inner wall of the injection needle A. A ring of rigidresin 6 plugs the tube 9 and together they form a spacer for the innerend of sensing mechanism 5. The rear end of ring 6' is closed leaving acentral forward bore seating the rear of sensing mechanism 5. The frontopen end of tube A is closed by a diaphragm 10 of thin metal plate, theouter diameter of which equals the inner diameter of the outer tube Aand by the filler 7 disposed over the front surface of the diaphragm 10and extending to the sharpened end of the outer tube A.

In FIGS. 1 and 2, the electrodes 2 of the strain sensing elements 3 areeach connected to lead wires ll, 11 which in turn pass entirely throughtube 1 and filler 4 and run to the rear end of the outer tube A throughthe spacer 6, 6. These lead wires ll, 11 are led to the outside of theouter tube A to form a bridge circuit (not shown) including the strainsensing elements 3, 3 which provide an electric output proportional tothe pressure exerted against the filler 4 in tube 1. In FIG. 2, numeral12 designates relatively heavy rigid wires, one end of each of which isembedded in the tube 9. These wires are connected to the lead wires Ill,11 and serve as lead-outs for connection of the strain sensing elements3, 3 in said external bridge circuit as well as supports for enablingthe insertion of the tube 9 into tube A during assembly.

In use of the transducers of FIGS. 1 and 2, the sharpened open end ofthe outer tube A is inserted through the skin of a person, or body, topierce a blood vessel as in an ordinary injection, the pressure of theblood in the vessel then being transmitted to the sensing mechanism 5through the filter 7 of the nonconstrictive resin. A force proportionalto the sectional area of tube I in relation to that of tube A in theplane perpendicular to the axis of the outer tube acts on the sensingmechanism 5 as a uniaxial compression force. Such uniaxial compressionforce is then transmitted to the strain sensing elements 3 through thefilling material 4, imparting compression 5 to them in theirlongitudinal direction. As a result, the strain sensing elements 3, 3incur a resistance variation due to piezoresistive effect proportionedto the force imparted by the strain thus produced and when the strainsensing elements are powered by an electric voltage in theaforementioned bridge, such resistance variation is converted to changesin current, or electric signals for detection of pressure in the bloodvessel.

In FIGS. 1 and 2, the sensing mechanism Sis subjected to an axial forceproportioned to the inside sectional area of the outer tube A in a planeperpendicular to the axial direction of the outer tube as previouslydescribed but in FIG. 2 the output of the sensing mechanism is increasedto correspond to the inner diameter of the outer tube A because of thediaphragm connected to both tube A and tube I. Said output is larger inthe transducer of the embodiment of FIG. 2 than in that of FIG. 1although the damage incurred on a body blood vessel may also be larger,particularly for the dimensions given in the example below.

The following are the examples of construction of the embodiments inFIGS. 1 and 2:

EXAMPLE 1 (Fig.1) 3O EXAMPLE 2 (Fig. 2)

Strain sensing elements, filling material and slender tube are the samein characteristics as shown in.Example Injection Needle or Outer Tube a:

Outer diameter 11.25 mm.

Inner diameter 0.650.9 mm. Slender Tube 1:

Outer diameter 0.5-0.6 mm.

Inner diameter 0.3 mm. Diaphragm 10: 0.03 mm. copper plate.

Rigid resin and nonconstrictive resin are the same as shown in Example1.

Upon inserting the transducer into a body, a large resistance is exertedon the pressure transducer since the tip end of the outer tubepenetrates through the outer skin of the body. Said insertion resistanceis applied as a uniaxial compression force of the sensing mechanism 5through the filler 7 which is composed of nonconstrictive resin.

Generally, the mechanical strength of the strain sensing elementconsisting of a single crystal of semiconductor is greater against acompression force than against a tension force and weakest to atransverse force so much as to be easily broken. Since the sensingmechanism 5 of FIGS. 1 and 2 is provided with a surrounding slender tube1 of resilient material, it can bear considerable insertion resistancebecause said slender tube 1 bears such insertion resistance and preventsthe strain sensing elements from being subjected to buckling and theinsertion resistance may act as a uniaxial compression force for thestrain sensing elements. For example, in case the allowable range ofstrain in the longitudinal direction of the strain sensing element 3 inthe above examples 1 and 2 is less than 3,000 X l0- (cm/cm), the maximumpressure of insertion resistance produced from the strain as convertedfor calculation is, for an outer tube of 0.8mm inner diameter, about I00kg/cm and, for an outer tube of 0.3mm inner diameter about 700 kg/cm tobe applied on the tip end of the transducer. Accordingly, if thepressure exerted on the nonconstrictive resin upon insertion of antransducer is less than that of said pressures, the detection part ofthe pressure transducer will not be destroyed.

Further, when a larger insertion resistance is applied on the sensingmechanism 5, an extreme constriction of the filling material may beavoided by adhesion of the filling material to the slender inner tube 1which is an advantage of the strain sensing element being prevented fromdeformation and capable of resisting the insertion resistance.

In FIG. 3 is shown another modified embodiment, an inner tube P beingadhesively secured to the inner peripheral wall face of the outer tube Ato withstand higher insertion resistance. One end of the sensingmechanism 5 is adhered to the rear surface of the diaphragm 10 and theother end of the strain transducer 5 is secured to the inner wall faceof the inner tube P by a spacer 6" composed of a rigid resin.

In the embodiment of FIG. 2, the filler 7 is composed of anonconstrictive resin and occupies all the open space at the front ofthe needle covering the front surface of the diaphragm 10 to thesharpened end of the outer tube A coaxially. The spacer 6 is providedwith several rigid wires 12 to aid in assembling the sensing mechanism 5in the outer tube.

Although the description hereinbefore made on the present inventionparticularly referred to the manner of detection of pressure in theliving body of man and animals, the injection is not limited in use forthe measurement of pressure in such living bodies, but also it isadapted widely for the detection of pressure in, or outside any pressuremedium in static condition as well as in dynamic variation.

Furthermore, the strain sensing elements of the sensing mechanism ofthis invention can use only one element for detecting pressure insteadof two elements as illustrated. Thus, it is possible to effect atemperature compensation by assembling two or four strain sensingelements of equivalent in temperature dependent conversioncharacteristics in a half bridge, or full bridge circuit, any change intemperature in the pressure medium does not affect the output from thisdevice. As shown in the embodiments described, a p-type and an ntypeelement used as a pair will serve to convert the pressure to an electricsignal in the most sensitive way.

Although certain specific embodiments of the invention have been showand described, it is obvious that many mod ification thereof arepossible. The invention, therefore, is not to be restricted exceptinsofar as is necessitated by the prior art and by the spirit of theappended claims.

We claim:

1. A transducer comprising a rigid outer tube sharpened to a point atone open end to which the pressure to be measured is applied, acylindrical sensing mechanism disposed within said outer tube andincluding at least one strain sensing element of semiconductive materialthereon, a resilient filling material closing said pointed open end ofsaid outer tube and securing one end of said sensing mechanism, and aspacer securing the other end of said sensing mechanism, and a spacersecuring the other end of said sensing mechanism to said outer tube toform a space between the outer peripheral surface of said sensingmechanism and the inner peripheral surface of said outer tube and todispose said sensing mechanism substantially parallel to the directionof said outer tube.

2. A transducer according to claim 1, wherein said sensing mechanism isprovided with a housing tube which forms the cylindrical outer wall ofsaid sensing mechanism, said strain sensing element being disposedparallel to the axial direction of said housing tube, and a fillingmaterial surrounds said strain sensing element completely occupying theinterior space of said housing tube.

3. A transducer according to claim 2, wherein is further provided adiaphragm having its outer periphery secured to the inner peripheralsurface of said outer tube, one end of said sensing mechanism beingsecured to said diaphragm and said filling material closing the pointedend of the outer tube and being disposed over the surface of saiddiaphragm and extend- Patent No.

Inventofls) (SEAL) Attest:

Signed and sealed this 4th day of EDWARD M.FLETCHER,JR. AttestingOfficer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION December29 1970 3,550,583 Dated Takewo Chiku et a1 It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Column 4 lines 66 and 67 cancel "and a spacer securing other end of saidsensing mechanism".

May 1971 WILLIAM E SCHUYLER, Commissioner of Pate:

